This invention relates to the fabrication of semiconductor devices.
The fabrication of certain semiconductor devices includes the step of etching channels in a semiconductor substrate. Notable among these devices are laser devices such as channel substrate buried heterostructure (CSBH) lasers. (See, for example, U.S. Pat. No. 4,660,208 issued to Johnston, Jr. et al.) A well-formed channel can be critical to good device performance. In most techniques presently employed, the channel is formed by use of an appropriate etch mask with an opening formed above the area of the substrate which will comprise the channel region. The exposed substrate is then typically etched by a chemical etchant, for example, a mixture of HCl and H.sub.3 PO.sub.4 when the substrate is InP. (See, for example, U.S. Pat. No. 4,595,454 issued to Dautremont-Smith, et al.)
Present techniques appear to be adequate. However, vapor etching is an attractive alternative since it is inherently cleaner than chemical etching. It also has the potential for lower cost and higher throughput in cases where it is desired subsequently to form various device layers by vapor growth, since etching and growth can be done in a single chamber. One major problem which exists in masked vapor etching, however, is the fact that the gas etchant tends to move along the mask surface and attack the exposed substrate in the channel openings. This increases the etch rate, thereby making control of the etching difficult. Attempts to solve this problem by reducing the amount of etchant have not been satisfactory, in general, since reducing the concentration below a certain value tends to produce rough channel sidewalls.
The same problem has also been found where it is desired to effect vapor growth in the exposed area of a masked substrate. That is, growth rate will be difficult to control since the reactants will tend to move along the mask surface.
It is, therefore, an object of the invention to control vapor etching of channels and/or vapor growth of material in a semiconductor substrate.